1. Field of the Invention
The aspects of the present disclosure relate generally to the field of light emitting electrical packages, and in particular to an organic light emitting diode package with energy blocking layers.
2. Description of Related Art
An Organic Light Emitting Diode (OLED) is a type of electroluminescent device in which light is generated within an organic compound formulated to emit light when electric current is applied. An OLED is commonly fabricated from two types of organic materials, small molecules and polymers. Commonly used small molecules include organometallic chelates, fluorescent and phosphorescent dyes and conjugated dendrimers. A second type of OLED is constructed from conductive electroluminescent or electro-phosphorescent polymers. These devices are sometimes referred to as Polymer Light Emitting Diodes (PLED) or Polymer Organic Light Emitting Diodes (P-OLED). Typical polymers used in P-OLED construction include electroluminescent derivatives of poly(p-phenylene vinylene) and polyfluorene or electro-phosphorescent materials such as poly(vinylcarbazole). Traditionally, the term OLED referred only to devices constructed from small molecules, however in recent years OLED has been used to refer to both small molecule and polymer type of devices. When referring to a specific type of organic material, SM-OLED is used to describe a Small Molecule Organic Light Emitting Diode, and P-OLED is used to refer to a Polymer Organic Light Emitting Diode. For the purposes of this disclosure the term Organic Light Emitting Diode and the acronym “OLED” is defined to refer generally to devices constructed using both types of organic material.
OLEDs are well known in the art and are typically built as a laminate on top of a suitable substrate material such as glass or a polymer. It is known that materials used in OLEDs can be degraded by exposure to water and/or oxygen and is accelerated with heat. Both device and packaging materials can also be degraded from exposure to many types of electromagnetic radiation. Therefore, OLEDs need to be carefully packaged to protect them from these environmental influences. It is also important to carefully design these packages so that the environmentally sensitive packaging materials are adequately protected.
The degradation of the materials used in OLEDs by environmental factors significantly reduces the life expectancy of such devices. Cathodes are often made of metals such as barium or calcium because their low work functions promote injection of electrons into the LUMO of the organic layer. These metals are highly reactive and degrade rapidly when exposed to water or oxygen. Other materials, such as the organic materials used in the emissive layers and transparent conductive films used in the anode, are also susceptible to degradation from environmental factors. Polymeric materials are sensitive to radiation and degrade when exposed to infrared (IR) radiation in the range of 0.6 to 1.3 electronvolt (eV) or ultraviolet (UV) radiation in the range of 3.4 to 5 eV. Polyethylene terephthalate (PET), often used as a substrate material, will yellow when exposed to UV radiation. In addition to causing damage, UV and IR radiation also exacerbate water penetration problems. Rigorous encapsulation of OLED devices is therefore required.
An OLED's efficient conversion of electricity to light makes it desirable for use in lighting applications in homes and buildings. Materials used in buildings are often designed with fire safety in mind and many building codes place combustibility requirements on building materials. Fire safety standards for large OLED panels intended for use as lighting in buildings and homes require that the combustibility of materials used be taken into account in the design of OLED panels.
There are several standards used for rating flame retardant properties of materials from organizations such as American Society for Testing and Materials (ASTM), Underwriters Laboratories (UL), International Organization for Standardization (ISO), or National Fire Protection Agency (NFPA). A widely used measure of the flammability of polymeric materials is the Limiting Oxygen Index (LOI). The LOI is defined as the minimum concentration of oxygen in a nitrogen/oxygen mixture required to just support candle like combustion of a test sample. Dry air contains slightly less than 21% oxygen, so a material requiring a concentration of more than 21% oxygen to support combustion (LOI>21) will tend to retard the spread of fire. Materials having a LOI of 21% or more are referred to as fire retardant materials. The LOI is standardized in the United States under ASTM D 2863 and internationally by ISO 4589. The LOI of some commonly used polymers is shown in Table 1.